Could you use the American PT boat crew, with some mods, it might serve your purpose. This should be good, hope it works and have fun.

I thought the mae west was an inflatable worn by aircrews. In most of the books I have, navy personel had a life jacket covered in cloth but filled with either feathers or the bock type with balsa wood. Also, pictures show many did not wear them but kept them close. Some combat areas would probably be tight fits, so some swimming without a vest on would be feasible mixture, as per combat footage of resues. Not my area of normal building so I might be wrong here.